Water Dissolving Salt
Solubility & Saturation
FILL IN HANDOUT AS WE GO…
Solubility
Solubility: maximum amount of solute that can be
dissolved in a given quantity of solvent at a specific
temperature.
Even for very soluble substances, there’s a limit to how
much can be dissolved in a given amount of solvent.
Saturation
Saturated solution: solution at the limit
◦Solution has as much solute as it can dissolve at that T
(temperature)
◦If more solute is added it won’t dissolve and will only
precipitate out
◦In a state of dynamic equilibrium: rate of dissolving = rate
of crystallizing
Saturation
Unsaturated solution: solution under the limit
◦Solution hasn’t reached the limit of how much solute it
can dissolve at that T
◦If more solute is added it will dissolve
Supersaturated solution: solution above the limit
◦Solution contains higher than saturation concentration of
solute
◦Any slight disturbance/seeding causes
crystallization/precipitation of excess solute
Supersaturation – needle structure
Supersaturation – seeding
Ex: At 20⁰C, solubility of NaCl(s) in water is 36g/100mL.
Saturation
Concentration ([ ]): quantitative measure (a number) of
how much solute is contained in an amount of solvent.
◦Ex:
Saturation
Concentrated solution: qualitative term; “large” amount of
solute dissolved.
Dilute solution: qualitative term; “small” amount of solute
dissolved.
Q: At 20⁰C, KCl(s) solubility is 34g/100g of
water. In the laboratory, a student mixes 45g
KCl(s) with 100g of water at 20⁰C.
A. How much KCl(s) will dissolve? ___________
B. Is the solution saturated? ___________
C. What is the mass in grams of solid KCl that won’t
dissolve? __________________________
Q: At 50⁰C, the solubility of NaNO3(s) is 114g/100g of
water. How many grams of NaNO3(s) are needed to make
a saturated solution of 50g of water at 50⁰C?
Practice!
Practice: p. 223 # 4-10, p. 226 #1-7, 9, 10
Read: p. 220-226
Flame Tests
Concentration
NOT THE TYPE YOU NEED FOR A TEST
Concentration
Concentration: quantitative measure of solute in solvent.
How much solute is dissolved in solvent. Can be represented
by different units, ∴ there are different ways of stating
concentration.
Most commonly used:
molar concentration or molarity = _________ = C
C=
Ex 1: What is the molar concentration of 4.00L
solution with 1.54mol NaOH in it?
Ex 2: What is the molarity of 0.23mol of
sodium sulphate dissolved in 500mL of water?
Ex 3: 4.00g of NaOH is dissolved in 250mL of
solution. What’s the molarity of NaOH(aq)?
Ex 4: How many mL of 0.400M NaOH solution
will contain 1.00g of NaOH?
Ex 5: How many moles are in 2.00L of
4.00mol/L solution of NaCl?
Ex 6: What is the mass of NaCl in the previous
example?
Ex 7: What’s the volume when 0.500 moles of
NaOH make a 3.00mol/L solution?
Ex 8: Calculate the mass of Na2CO3 required to
make 3.5L of a 1.2mol/L solution.
Ex 9: What volume of 0.500M solution can be
made from 12.00g of NaCl?
Ex 10: What’s the concentration of a solution
with 53.2g of CaCl2 in 5000mL of water?
Other Concentration Calculations
(% mass, % volume, ppm)
Percent by mass:
Percent by volume:
Ex: What’s the % by mass of NaCl if 9.0g of
NaCl is added to 91.0g of water?
Ex: What’s the % by volume of ethanol if
15.0mL of ethanol is added to 85.0g of water?
Parts per Million (ppm)
Parts per million (ppm): same units top and bottom multiplied by a million (106)
◦ Useful for very low concentrations
Ex: What is the ppm (m/v) of NaCl if 5.9mg of
NaCl is dissolved in 500mL of water?
Concentration of Ions in Solution
1. Write a balanced dissociation equation or ionization
equation:
Ex: Al2(SO4)3(aq)
2. Use the mole ratio and the Factor-Label Method to find
the concentration of the ions:
Ex: 1.00M Al2(SO4)3(aq). Find [Al3+] and [SO42-].
Ex: 1.00M Al2(SO4)3(aq). Find [Al3+] and [SO42-].
Ex: A barium hydroxide solution is 2.00mol/L.
Find [Ba2+] and [OH-].
Practice!
Practice: p. 316 #1-4, 6, p. 214 #2-12, 15
Read: p. 314-215, p. 203-213
Strengths/Weaknesses of Acids/Bases
Bronsted-Lowry A/B
Ionization/Dissociation
Equations
FILL IN THE HANDOUT AS WE GO…
How to write equations for ACIDS:
General Equation: HA donates H+ (proton) to H2O (acts as a
base):
How to write equations for ACIDS:
Therefore, a conjugate acid-base pair consists of two substances
related to each other by donating/accepting a proton (H+).
Ex:
How to write equations for ACIDS:
The hydronium ion (H3O+) forms from attraction between
H+ and polar H2O. Both H3O+ and H+ are used to measure
the strength of an acid (they are used interchangeably).
Practice: Identify the conjugate acid-base
pairs in the following equations:
1.
2.
Practice: Identify the conjugate acid-base
pairs in the following equations:
3.
4.
Practice: Identify the conjugate acid-base
pairs in the following equations:
5.
6.
Polyprotic Acids!
The last 3 equations are examples of polyprotic acids!
◦ Polyprotic acids can lose more than one proton (H+):
◦ Ex:
◦ Ex:
So they can react with H2O more than once to produce many H3O+!
◦ # times an acid can react = # H’s at the front; each time it reacts, it
gets weaker
Favouring Stronger Products
In all of the above equations, the products are stronger
acids and bases than the reactants. Remember: strong acids
completely ionize. Weaker acids don’t and we can represent
this with a forward and reverse arrow.
Ex:
How to write equations for BASES:
1. If it has an OH- (hydroxide): simply write the dissociation
equation
◦General Equation: (these are strong bases!)
Ex: NaOH(aq)
How to write equations for BASES:
2. If it has no OH- (hydroxide): split the cmpd into its ions
and use the anion (-ve one).
◦React the anion with H2O to produce OH◦Determine the other product (it’s the anion gaining a H+).
Remember: acids lose H+, bases gain H+
◦General Equation: (these are weak bases!)
Ex: Na2CO3
Ex: Na3PO4
Ex: NH3
Polyprotic Bases
Polyprotic bases: can accept more than one proton
(H+) so it can react with H2O many times to produce
many OH- (hydroxide ions):
◦Ex:
◦Ex:
# times it can react = # charge
Strong vs. Weak Acids/Bases:
The stronger the acid, the more H3O+ it produces, the
higher its [H3O+], and the more forward the ionization
moves (>99% ionization):
◦General Equation:
◦(There are 7 strong acids and they’re listed on the data
sheet)
Strong vs. Weak Acids/Bases:
The stronger the base, the more OH- it produces, the
higher its [OH-], and the more forward the dissociation
moves (>99% dissociation):
◦General Equation:
◦(Strong bases: have OH- and a Group 1 metal/Alkali
metal)
Strong vs. Weak Acids/Bases:
Weak acids and bases only partially ionize and dissociate
(<50%):
◦General Equation:
Strong vs. Weak Acids/Bases:
So the reverse process dominates over the forward process:
Strong vs. Weak Acids/Bases:
◦General Equation (weak acid):
◦General Equation (weak base):
Dissociation of strong/weak acids
pH Scale Practice!
FILL IN THE HANDOUT AS WE GO…
1. How many significant digits/figures are
there?
a) pH = 10.01 __________ sig figs
b) pH = 7.3 __________ sig figs
c) 0.0034mol/L __________ sig figs
-10
d) 5.60 x 10 M __________ sig figs
2. What’s the pH?
Formula:
a)
b)
c)
d)
e)
f)
Hydronium ion concentration of 5.1 x 10-6mol/L?
pH = __________
[H+] = 1.32x10-3M pH = __________
[H3O+] = 3.05x10-6mol/L pH = __________
[H+] = 1.7x10-8M pH = ___________
[H3O+] = 4.500x10-7mol/L pH = ___________
[H+] = 2.6x10-12M pH =____________
+
3. What’s the [H3O ]?
Formula:
a)
pH = 0.89 [H3O+] = ______________________
b)
pH = 5.3 [H3O+] = _______________________
c)
pH = 1.370 [H3O+] = _____________________
d)
pH = 9.00 [H3O+] = ______________________
e)
pH = 13.014 [H3O+] = ____________________
4. pH of 0.152M HBr(aq)?
5.
-4
pOH of 3.5x10 M HCl(aq)?
6. pOH of 0.040M H2SO4(aq)?
7.
+
pOH, [H ] and pH of 0.100M NaOH(aq)?
8. Calculate [H+] and pH of 0.002M Ca(OH)2(aq).
9. Calculate [H+] and pH of 8.5x10-5M LiOH(aq).
HCl & NaOH rxn with Universal Indicator